Chlorella: What It Is and How It Works

Chlorella is one of the best-known microalgae on the dietary supplement market, especially popular in Japan and Korea. It is often placed on a par with spirulina, although biologically they are completely different organisms. The editors explain what chlorella is, what it is made of, how it may affect the body, and what of this is confirmed by human studies.

What chlorella is

Chlorella (Chlorella) is a genus of single-celled green algae a few micrometers in diameter. Unlike spirulina, which is a cyanobacterium (a prokaryote), chlorella is a true eukaryotic cell with a nucleus, a chloroplast, and a sturdy cell wall. The most common species in supplements areChlorella vulgarisandChlorella pyrenoidosa(in modern taxonomy some strains have been reassigned to other names).

Interest in chlorella as food arose in the mid-20th century: it was considered a promising source of protein for humanity because of its high growth rate. Industrial production developed in Japan and Taiwan, where chlorella is still among the most popular supplements.

Chlorella is grown in open ponds or closed fermenters. Some strains are cultivated heterotrophically — on glucose in the dark; such biomass has a different color and pigment composition than chlorella grown in the sun.

After harvesting, the biomass is dried and, as a rule, subjected to mechanical or other processing to break down the cell wall. It is precisely this technological step that fundamentally distinguishes chlorella from spirulina and affects its digestibility.

Composition: how chlorella differs from spirulina

In terms of composition, chlorella is a protein-rich product: in the dry mass, protein usually accounts for about half, the rest being carbohydrates, lipids, minerals, and pigments. Chlorella is notable for a very high content of chlorophyll, as well as carotenoids (lutein) and vitamin K.

An important difference from spirulina is vitamin B12. Studies by Watanabe's group showed that some chlorella products contain the active form of B12, whereas in spirulina the inactive pseudovitamin predominates. However, the content varies greatly between products, and there is a suggestion that the B12 in chlorella may come from bacteria accompanying the culture.

A specific component of chlorella that is often mentioned is the so-called “chlorella growth factor” (CGF), an extract rich in nucleotides and peptides. The marketing claims about it far outpace the scientific data.

Overall, both algae are nutritious but have different “strengths,” so they should not be considered interchangeable.

Cell wall and digestibility

Chlorella's cell wall consists of cellulose and other resistant polysaccharides and is poorly digested in the human gastrointestinal tract. If the cells remain intact, a significant part of the nutrients is simply not released.

So manufacturers use methods of breaking down the wall: mechanical grinding, pressure treatment, enzymatic methods. On the packaging this is indicated as “broken cell wall.”

The rigid cell wall has another side: it is associated with chlorella's ability to bind certain compounds in the intestine. This underlies the hypotheses about “detoxifying” properties, which, however, have been studied mainly in animals.

The practical conclusion: when choosing a product, look for a “broken cell wall” mark, otherwise the benefit of taking it may be minimal.

How chlorella may affect the body

The immune system. In a randomized placebo-controlled study by Kwak et al. (2012) in healthy Korean adults, 8 weeks of taking chlorella increased the activity of natural killer cells and changed the levels of some cytokines. Otsuki et al. (2012) reported that in participants of an intensive kendo training camp chlorella mitigated the decline in secretory IgA in saliva — a marker of mucosal protection.

The cardiovascular system. Merchant and Andre (2001), in a review of their own clinical work, described a possible effect of chlorella on blood pressure in patients with mild hypertension, although the studies were small and without full control. There are also data from small studies on blood lipids.

Physical performance. Umemoto and Otsuki (2014) found an increase in peak oxygen uptake in young people after 4 weeks of taking chlorella. This is an interesting but isolated result; we examine it in more detail in a separate article on the evidence base for athletes.

• Antioxidant action:carotenoids, chlorophyll, vitamins C and E;
• Immunomodulation:polysaccharides and glycoproteins of the cell wall;
• Binding of compounds in the intestine:a hypothesis, data mostly preclinical;
• Nutrient contribution:protein, iron, folate, B12 (varies).

Reviews by Panahi et al. (2016) and Bito et al. (2020) summarize that chlorella has a variety of potential effects, but most clinical studies are small, short, and require confirmation.

Safety and who should be cautious

Chlorella is generally well tolerated. The most common side effects are bloating, nausea, and a change in stool color to green, especially in the first days of use.

Because of its high vitamin K content, chlorella can affect the action of warfarin. Isolated cases of photosensitivity associated with chlorophyll breakdown products, as well as allergic reactions, have also been described.

As with spirulina, the immunostimulating properties call for caution in autoimmune diseases and during immunosuppressant therapy.

Product quality is a key factor: control of heavy metals, microbiological indicators, and pheophorbide content should be confirmed by the manufacturer.

Editors' conclusions

Chlorella is a single-celled green alga, rich in protein, chlorophyll, carotenoids, and vitamin K; some products also contain active B12.

Its rigid cell wall limits absorption, so it is important to choose products with a broken cell wall.

Clinical data point to a possible effect on immune markers, blood pressure, and aerobic performance, but the studies are small.

To continue the topic, our articles “Chlorella Benefits for Athletes: The Evidence Base,” “Chlorella Side Effects,” and “Myths About Spirulina” will help.

References

1. Bito T, Okumura E, Fujishima M, Watanabe F. Potential of Chlorella as a dietary supplement to promote human health. Nutrients. 2020;12(9):2524.
2. Panahi Y, Darvishi B, Jowzi N, Beiraghdar F, Sahebkar A. Chlorella vulgaris: a multifunctional dietary supplement with diverse medicinal properties. Curr Pharm Des. 2016;22(2):164–173.
3. Kwak JH, Baek SH, Woo Y, et al. Beneficial immunostimulatory effect of short-term Chlorella supplementation: enhancement of natural killer cell activity and early inflammatory response (randomized, double-blinded, placebo-controlled trial). Nutr J. 2012;11:53.
4. Otsuki T, Shimizu K, Iemitsu M, Kono I. Chlorella intake attenuates reduced salivary SIgA secretion in kendo training camp participants. Nutr J. 2012;11:103.
5. Umemoto S, Otsuki T. Chlorella-derived multicomponent supplementation increases aerobic endurance capacity in young individuals. J Clin Biochem Nutr. 2014;55(2):143–146.
6. Merchant RE, Andre CA. A review of recent clinical trials of the nutritional supplement Chlorella pyrenoidosa in the treatment of fibromyalgia, hypertension, and ulcerative colitis. Altern Ther Health Med. 2001;7(3):79–91.
7. Watanabe F, Takenaka S, Kittaka-Katsura H, Ebara S, Miyamoto E. Characterization and bioavailability of vitamin B12-compounds from edible algae. J Nutr Sci Vitaminol (Tokyo). 2002;48(5):325–331.
8. Kay RA. Microalgae as food and supplement. Crit Rev Food Sci Nutr. 1991;30(6):555–573.